Mirroring problem

[Kagu]

While I was working on one of my ships' engines, I parented the structure to the core and mirrored it, instead of manually building both halves of the engine. Now, I've moved the engine back to the left where it belongs, but when I mirror, it doesn't mirror to the other side because both halves have already been mirrored. As a last resort, I could just clone the entire half over again with the engine and delete the old one, but that would result in some depth errors because of some of my supports. Is there another way to fix this?